Regional distribution of large blowdown patches across Amazonia in 2005 caused by a single convective squall line

Abstract

In mid‐January 2005 a convective squall line traversed 4.5 × 106 km2 of Amazonia from southwest to northeast. As seen in Landsat images, this atypical convective storm left blowdown imprints with diffuse geometry, unlike the fan‐shaped wind disturbance of much more frequent east‐to‐west propagating squall lines. Previous work reported 0.2% of the forest area damaged by this one relatively rare event within one Landsat image and assumed similar disturbance across the entire traverse. We mapped convective wind damage impact to the region in 2005 by identifying large‐scale (>4 ha) blowdown imprints in 30 Landsat images. The diffuse‐type imprints associated with this single squall line contributed up to 60–72% of total 2005 wind‐disturbed area detected across the region, but damage was highly concentrated in central Amazonia. Consequently, the distribution of large wind damage patches in 2005 across Amazonia was very different from long‐term average. Regional distribution of wind‐driven tree mortality for smaller patch sizes remains unknown.

Strong temporal variation in treefall and branchfall rates in a tropical forest is explained by rainfall: results from five years of monthly drone data for a 50-ha plot

“…The few studies that have quantified temporal variation of tree mortality at monthly and bimonthly scales using ground-based data have all found higher tree mortality in times of higher rainfall (Brokaw, 1982;Fontes et al, 2018;Aleixo et al, 2019). This is consistent with the understanding that many trees die in treefalls, which are proximately caused by trunk breakage or uprooting, and are associated with storms (Marra et al, 2014;Araujo et al, 2017;Fontes et al, 2018;Negrón-Juárez et al, 2018;Esquivel-Muelbert et al, 2020). The collection of additional high temporal resolution mortality data over large areas, together with high temporal resolution climatological data, can aid in linking mortality to particular climatic events and thereby elucidating mortality mechanisms (Arellano et al, 2019;McMahon et al, 2019).…”

Windthrows control biomass patterns and functional composition of Amazon forests

“…In contrast to most human disturbances, windthrows do not alter the seed and seedling/sapling banks and retain nutrients via the incorporation of recalcitrant fractions of necromass into the soil (dos Santos et al, ; Vitousek & Denslow, ). Furthermore, windthrows, unlike logging, have a complex geometry (Araujo et al, ; Marra et al, ; Nelson et al, ). A higher perimeter per area of disturbed forest creates a more effective interface with adjacent undisturbed forest patches acting as seed sources.…”

“…Briefly, we identified windthrows occurring over a 20‐year period (1984–2005) using Landsat 5 Thematic Mapper imagery (L5, 30 m × 30 m resolution) (Chambers et al, ). Windthrows were identified by their spectral characteristics and distinct shape (Araujo, Nelson, Celes, & Chambers, ; Chambers et al, ; Nelson et al, ). After excluding data with cloud cover, white‐sand and floodplain forests, and forests close to human‐affected areas (e.g., roads and settlements), we identified sites integrating large‐scale single events (i.e., several windthrows created at the same time).…”

“…Such undisturbed areas were used as references for “pre‐disturbance” forest conditions for our response variables. Using transects allowed us to account for the pixel‐level variation in windthrow tree‐mortality, size, and geometry of gaps (Araujo et al, ; Marra et al, ; Negrón‐Juárez et al, ) while keeping fieldwork logistically feasible. Hence, transects include local variation in topography and a wide range in windthrow tree mortality, ranging from undisturbed subplots to subplots with 70% windthrow tree mortality (Magnabosco Marra, ; Marra et al, ; Negrón‐Juárez et al, ).…”

Fire, fragmentation, and windstorms: A recipe for tropical forest degradation

“…Downbursts associated with convective systems that produce strong vertical descending wind gusts are particularly noteworthy because their effects range from the breakage of individual branches or single treefalls to blowdowns of thousands of hectares (Garstang, White, Shugart, & Halverson, ; Nelson, Kapos, Adams, Oliveira, & Braun, ). For example, a squall line that moved from SW to NE Amazonia in 2005 damaged extensive forested areas (Negrón‐Juárez et al, ) especially in central Amazonia, although the number of damaged trees remains uncertain (Araujo, Nelson, Celes, & Chambers, ). Wind impacts on closed forest canopies are known to vary with storm strength (Canham, Thompson, Zimmerman, & Uriarte, ), topography (de Toledo, Magnusson, Castilho, & Nascimento, ; Rifai et al, ), and tree structural characteristics such as wood density (Putz, Coley, Lu, Montalvo, & Aiello, ; Rifai et al, ), whole‐tree flexibility (Asner & Goldstein, ), height–diameter ratio (Hurst, Allen, Coomes, & Duncan, ), and size (Rifai et al, ).…”